1. Field of the Invention
The present invention relates to a method of preparing a double layered, palladium-only three-way catalyst using composite oxides, more particularly to a method of preparing a double layered, palladium-only three-way catalyst comprising a first coating layer (bottom layer) and a second coating layer (top layer) containing palladium by incorporating composite oxide, praseodymium oxide, and perovskite.
2. Description of Related Art
In general, a three-way catalyst refers to a catalyst that facilitates the removal of the noxious components from automobile exhaust gas, such as hydrocarbons, carbon monoxide and nitrogen oxide (Nox). Conventional three-way catalysts have included Pt/Rh, Pd/Rh or Pt/Pd/Rh.
These conventional catalysts use rhodium (Rh) to reduce Nox in the exhaust gas, which presents some disadvantages. The use of rhodium is expensive. In addition, rhodium exhibits poor heat resistance.
Moreover, palladium-only three-way catalysts (i.e., single layer coated catalysts) without using rhodium have been reported in Korea Patent Registration Publication No. 235029 and U.S. Pat. No. 6,043,188 entitled “Process for Manufacturing Palladium Ternary Catalyst,” which are both incorporated herein by reference in their entireties. The process for preparing such catalysts begins by impregnating a palladium solution with alumina (Al2O3), which is then reduced. Next, cerium oxide (CeO2) and a mixing solution are added. The pH of the resulting mixture is adjusted and allowed to react. Then, the mixture is milled to obtain a catalyst slurry. Finally, a ceramic monolith is dipped in the prepared catalyst slurry, dried and calcined to produce a palladium-only three-way catalyst.
Recently, regulations on automobile exhaust gas have become more stringent thereby necessitating the use of improved catalysts with superior heat resistance. To meet these requirements, precious metals have been increasingly used as raw materials for catalysts, which has increased costs.
Accordingly, development of a three-way catalyst that can reduce the amount of precious metals to be used, while offering superior removal of Nox and heat resistance, is highly desired.